There is widespread use of cars equipped with airbag devices for protecting occupants in the driver's seat and the passenger seat in a vehicle collision or in an emergency. The airbag devices are installed in, for example, the steering wheel and the instrument panel and have airbags that are inflatable and deployable. Furthermore, in recent years, knee-protecting airbag devices that can protect, at least, the knees of occupants are employed. In order to protect mainly the knees of the occupant, the airbag device is disposed in the vehicle body in front of the occupant, and the inflator is activated in a vehicle collision or in an emergency to inflate and deploy the airbag (a so-called knee bag or knee airbag) mainly between the vehicle body and the knees of the occupant.
This knee-protecting airbag device is disposed in, for example, a lower part of the instrument panel in front of the occupant. From there, in order to protect the occupant, the airbag is inflated and deployed toward a narrow space between the vehicle body and the occupant's legs up to the vicinity of the knees of the occupant before the knees of the occupant come into contact with the vehicle body. Therefore, knee-protecting airbag devices are required to have faster deployment characteristics; for example, the airbags need to deploy up to a height above the knees of the occupant within a short period of time (about 10ms (milliseconds)) after the airbag starts to inflate and deploy. At the same time, if the airbag exerts a force in directions spreading the knees of the occupant apart during inflation and deployment, the injury to the occupant would be significant, which is dangerous. Therefore, the airbag is also required to deploy evenly on the left and right sides, while preventing the occupant from coming into contact with the airbag deploying in a lateral direction.
In order to meet such a requirement, conventionally, a knee-protecting airbag device is known in which gas supplied from an inflator to the airbag is distributed to both sides in the lateral direction (the left-right direction) of the vehicle using a gas-flow distribution cloth to prevent the central portion of the airbag from inflating and deploying and to improve the inflation and deployment performances at ends in the left-right direction of the airbag, allowing the airbag to rapidly enter in front of the knees of the occupant (see Japanese Patent No. 3687602).
However, with this conventional knee-protecting airbag device, depending on the type of the inflator to be used or the manner in which the inflator is disposed in the airbag, the deployment characteristics of the airbag may decrease. That is, for example, a tubular inflator used in this airbag device usually has a gas discharge port at one end in the lengthwise direction. Therefore, if this inflator is disposed in such a manner that the center thereof is aligned with the center of the airbag in the lateral direction, the gas discharge port at one end is positioned so as to face an end of the gas-flow distribution cloth located off the center. As a result, the gas generated from the inflator may be supplied unevenly to one side in the airbag, making the deployment of the airbag uneven in the left and right directions. On the other hand, in order to counter this, if the inflator is disposed so as to be shifted in the lateral direction in the airbag to make the gas discharge port be aligned with the center of the airbag, the disposition thereof in the airbag becomes difficult. This makes it difficult to assemble the inflator with the airbag, decreasing the working efficiency in the assembling. Furthermore, in this case, a problem of decrease in the balance of the airbag device in the left-right direction occurs.
In addition, in this conventional knee-protecting airbag device, because the gas generated by the inflator is directly blown against the gas-flow distribution cloth and the airbag, the heat may make a hole and damage the gas-flow distribution cloth and the airbag. Similarly, in this airbag device, because the gas discharge port of the inflator is directly in contact with the airbag, the airbag, including the internal members, may be more likely to be damaged during inflation and deployment; for example, the heat generated by the gas generation in the vicinity thereof may make a hole in the airbag.
[Patent Document 1] Japanese Patent No. 3687602